Final grit before sealer

Gentlemen,

Would the excellent comments and recommendations in this thread apply to a SS acrylic urethane? I know that 99% of the posts on the SPI forum apply to BC/CC but I have decided to use a SS acrylic urethane for my top coat on the ’55 Studebaker. The tech sheet recommends P320 and my vo tech instructor recommends P400. The P400 is in line with what most of you have recommended for solid color base coats. My plan is to use the reduced SPI epoxy primer as a seal coat. I am hoping it can be applied also as a first coat under the SS similar to base coat.

Charlie D.
 
I usually use 800-1000 for denibbing between coats of base, 600 for denibbing sealer

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Charlie D;34638 said:
Gentlemen,

Would the excellent comments and recommendations in this thread apply to a SS acrylic urethane? I know that 99% of the posts on the SPI forum apply to BC/CC but I have decided to use a SS acrylic urethane for my top coat on the ’55 Studebaker. The tech sheet recommends P320 and my vo tech instructor recommends P400. The P400 is in line with what most of you have recommended for solid color base coats. My plan is to use the reduced SPI epoxy primer as a seal coat. I am hoping it can be applied also as a first coat under the SS similar to base coat.

Charlie D.
Click to expand...

If it's a solid color 320 or 400 before sealer will work fine.
 
I am going to be spraying SPI epoxy followed by SPI black base and Universal clear soon. I blocked the whole truck (sprayed in Turbo primer) in 320 dry followed by 400 on a soft interface pad by hand. I was debating stepping out to 600 wet, but I may stop at 400 if the epoxy will cover well. I went over some tough to reach areas with a gray 3m scotch brite pad and it almost seemed to polish the turbo primer. I'm wondering if I should switch to a red 3m scotch brite before the sealer goes down? Any thoughts on that?
 
I think most grey scuff pads are equal to around 800 grit. 800 is fine but will still work perfectly fine-plenty coarse enough for sealer or topcoat adhesion. This whole thread has been about what grit people can get away with using and we pointed out that the requirements differ depending on if the color is a solid or metallic, basecoat or singlestage. Confusing I bet but it all makes sense once you spend some time doing it.
 
That's good to know.....form what I'm getting out of this

If that were not sealer and it was straight primer......a red pad would be required?
Sealer is thinner than straight primer....almost like base. 400 for solids and 600 for metallic or a gray scotch Brite for sealer to top coat
Gray scotch Brite is 800 which is the last of the grits you should use to get good adhesion....but most stop at 600

Question.....when the gray pad is new it's 800. What happens when it dulls and you get an inconsistent scratch?
Then you have scratches of 800 and 1000 because of the dull pad?
Either way it makes sense because I've always heard you rough up clear with a gray pad to put paint on top of it. I always found that confusing because everyone likes that 400 to 600 scratch for a base in primer....but then you can go with 800 to 1000 in clear........and in primer to put sealer over it.

Your right about spending some time doing it. Helps a lot.........i do over think things a lot but i have made some very time consuming expensive mistakes leading me to wanting to know the why of things as opposed to the procedure

Even looking at the post above where he flattened the primer with 320 but said nothing about cutting it with 180. Did he miss the step......he will haVe wavy panels with just 320? He probably cut it with 120 or 180 but doesn't say
The reason I point this out is because on my last paint job I did the same thing.....sprayed the high build and flattened it straight with 320. I didn't know about the 180, fortunately it was on a motorcycle and had very little surface area.

Also will ANY high build primer stick new or dull red pad scratches to recoat with more high build? I've got some nooks that are a real pain to get to. I know it will work with most high builds....mine is marhyde
And the tech sheet doesn't say http://multimedia.3m.com/mws/mediawebserver?mwsId=66666UF6EVsSyXTtNxMyLXM6EVtQEVs6EVs6EVs6E666666--
 
Personally I would be hesitant to use anything coarser than 320 when sanding my final primer coats. That's just me though. 320 cuts really well IMO. My regimen is to cut the final primer coats with 320 dry on a hard block, then 400 dry on a soft block, 600 wet on a soft block, then grey scotch brite. May be overkill, but I've never seen a single sand scratch come back in the final product.
180 grit woulddef cut well, but I'd be afraid id miss a scratch or two and kick myself later
 
I think the conditions you paint in also might sway how you do your final steps. I don't have a booth so I whip up a makeshift plastic tent for final color and clear. So after the final 320 sand of primer, I lay on 2 coats of epoxy with just a splash of reducer so it lays flat but has a little build to it. This gives me a little extra insurance that any filler that was showing though primer doesn't bleed and will fill any minor sand scratches I missed. Then I'll wet sand this with a 600 before shooting the metallic. Only after all sanding is done I'll prep and put up the plastic for a booth. The way I figure it, the fewer coats that get laid down as a final finish without any sanding (I try not to touch metallic between coats), the less chance of getting trash in it. That's why I treat the epoxy as a primer coat and a sealer before paint.

I just laid down two final coats of epoxy yesterday on this cobra, hope to shoot the color this coming weekend.

IMG_20140316_153136_363.jpg
 
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